Conductive inks containing pyridine compounds

ABSTRACT

Disclosed is an ink composition comprising (a) an ink vehicle which comprises a conductive pyridinium compound having a melting point of no lower than about 60° C. and no higher than about 155° C., (b) a viscosity modifier which is a pyridine compound, a pyrimidine compound, a pyrazine compound, a pyridazine compound, or mixtures thereof, said pyridine, pyrimidine, pyrazine, or pyridazine compounds having a melting point of no lower than about 60° C. and no higher than about 155° C., (c) a binder which is a polymeric pyridine or pyridinium compound; (d) a colorant, (e) an optional antioxidant, and (f) an optional UV absorber.

BACKGROUND OF THE INVENTION

The present invention is directed to hot melt ink compositions. Morespecifically, the present invention is directed to ink compositionssuitable for use in hot melt acoustic ink printing processes,particularly those in which conductive inks are desirable. Oneembodiment of the present invention is directed to an ink compositioncomprising (a) an ink vehicle which comprises a conductive pyridiniumcompound having a melting point of no lower than about 60° C. and nohigher than about 155° C., (b) a viscosity modifier which is a pyridinecompound, a pyrimidine compound, a pyrazine compound, a pyridazinecompound, or mixtures thereof, said pyridine, pyrimidine, pyrazine, orpyridazine compounds having a melting point of no lower than about 60°C. and no higher than about 155° C., (c) a binder which is a polymericpyridine or pyridinium compound; (d) a colorant, (e) an optionalantioxidant, and (f) an optional UV absorber.

Acoustic ink jet printing processes are known. In acoustic ink jetprinting processes, an acoustic beam exerts a radiation pressure againstobjects upon which it impinges. Thus, when an acoustic beam impinges ona free surface (i.e., liquid/air interface) of a pool of liquid frombeneath, the radiation pressure which it exerts against the surface ofthe pool may reach a sufficiently high level to release individualdroplets of liquid from the pool, despite the restraining force ofsurface tension. Focusing the beam on or near the surface of the poolintensifies the radiation pressure it exerts for a given amount of inputpower. These principles have been applied to prior ink jet and acousticprinting proposals. For example, K. A. Krause, “Focusing Ink Jet Head,”IBM Technical Disclosure Bulletin, Vol. 16, No. 4, September 1973, pp.1168-1170, the disclosure of which is totally incorporated herein byreference, describes an ink jet in which an acoustic beam emanating froma concave surface and confined by a conical aperture was used to propelink droplets out through a small ejection orifice. Acoustic ink printerstypically comprise one or more acoustic radiators for illuminating thefree surface of a pool of liquid ink with respective acoustic beams.Each of these beams usually is brought to focus at or near the surfaceof the reservoir (i.e., the liquid/air interface). Furthermore, printingconventionally is performed by independently modulating the excitationof the acoustic radiators in accordance with the input data samples forthe image that is to be printed. This modulation enables the radiationpressure which each of the beams exerts against the free ink surface tomake brief, controlled excursions to a sufficiently high pressure levelfor overcoming the restraining force of surface tension. That, in turn,causes individual droplets of ink to be ejected from the free inksurface on demand at an adequate velocity to cause them to deposit in animage configuration on a nearby recording medium. The acoustic beam maybe intensity modulated or focused/defocused to control the ejectiontiming, or an external source may be used to extract droplets from theacoustically excited liquid on the surface of the pool on demand.Regardless of the timing mechanism employed, the size of the ejecteddroplets is determined by the waist diameter of the focused acousticbeam. Acoustic ink printing is attractive because it does not requirethe nozzles or the small ejection orifices which have caused many of thereliability and pixel placement accuracy problems that conventional dropon demand and continuous stream ink jet printers have suffered. The sizeof the ejection orifice is a critical design parameter of an ink jetbecause it determines the size of the droplets of ink that the jetejects. As a result, the size of the ejection orifice cannot beincreased, without sacrificing resolution. Acoustic printing hasincreased intrinsic reliability because there are no nozzles to clog. Aswill be appreciated, the elimination of the clogged nozzle failure modeis especially relevant to the reliability of large arrays of inkejectors, such as page width arrays comprising several thousand separateejectors. Furthermore, small ejection orifices are avoided, so acousticprinting can be performed with a greater variety of inks thanconventional ink jet printing, including inks having higher viscositiesand inks containing pigments and other particulate components. It hasbeen found that acoustic ink printers embodying printheads comprisingacoustically illuminated spherical focusing lenses can print preciselypositioned pixels (i.e., picture elements) at resolutions which aresufficient for high quality printing of relatively complex images. Ithas also been discovered that the size of the individual pixels printedby such a printer can be varied over a significant range duringoperation, thereby accommodating, for example, the printing of variablyshaded images. Furthermore, the known droplet ejector technology can beadapted to a variety of printhead configurations, including (1) singleejector embodiments for raster scan printing, (2) matrix configuredejector arrays for matrix printing, and (3) several different types ofpagewidth ejector arrays, ranging from single row, sparse arrays forhybrid forms of parallel/serial printing to multiple row staggeredarrays with individual ejectors for each of the pixel positions oraddresses within a pagewidth image field (i.e., singleejector/pixel/line) for ordinary line printing. Inks suitable foracoustic ink jet printing typically are liquid at ambient temperatures(i.e., about 25° C.), but in other embodiments the ink is in a solidstate at ambient temperatures and provision is made for liquefying theink by heating or any other suitable method prior to introduction of theink into the printhead. Images of two or more colors can be generated byseveral methods, including by processes wherein a single printheadlaunches acoustic waves into pools of different colored inks. Furtherinformation regarding acoustic ink jet printing apparatus and processesis disclosed in, for example, U.S. Pat. No. 4,308,547, U.S. Pat. No.4,697,195, U.S. Pat. No. 5,028,937, U.S. Pat. No. 5,041,849, U.S. Pat.No. 4,751,529, U.S. Pat. No. 4,751,530, U.S. Pat. No. 4,751,534, U.S.Pat. No. 4,801,953, and U.S. Pat. No. 4,797,693, the disclosures of eachof which are totally incorporated herein by reference. The use offocused acoustic beams to eject droplets of controlled diameter andvelocity from a free-liquid surface is also described in J. Appl. Phys.,vol. 65, no. 9 (May 1, 1989) and references therein, the disclosure ofwhich is totally incorporated herein by reference.

In acoustic ink printing processes, the printhead produces approximately2.2 picoliter droplets by an acoustic energy process. The ink underthese conditions preferably displays a melt viscosity of from about 1 toabout 25 centipoise at the jetting temperature. In addition, once theink has been jetted onto the printing substrate, the image thusgenerated preferably exhibits excellent crease properties, and isnonsmearing, waterfast, of excellent transparency, and of excellent fix.The vehicle preferably displays a low melt viscosity in the acoustichead while also displaying solid like properties after being jetted ontothe substrate. Since the acoustic head can tolerate temperaturestypically up to about 180° C., the vehicle for the ink preferablydisplays liquid-like properties (such as a viscosity of from about 1 toabout 25 centipoise) at a temperature of from about 75 to about 180° C.,and solidifies or hardens after being jetted onto the substrate suchthat the resulting image exhibits a hardness value of from about 0.1 toabout 0.5 millimeter (measured with a penetrometer according to the ASTMpenetration method D1321).

Ink jet printing processes that employ inks that are solid at roomtemperature and liquid at elevated temperatures are known. For example,U.S. Pat. No. 4,490,731, the disclosure of which is totally incorporatedherein by reference, discloses an apparatus for dispensing solid inksfor printing on a substrate such as paper. The ink vehicle is chosen tohave a melting point above room temperature so that the ink, which ismelted in the apparatus, will not be subject to evaporation or spillageduring periods of nonprinting. The vehicle selected possesses a lowcritical temperature to permit the use of the solid ink in a thermal inkjet printer. In thermal ink jet printing processes employing thesephase-change inks, the solid ink is melted by a heater in the printingapparatus and used as a liquid in a manner similar to that ofconventional piezoelectric or thermal ink jet printing. Upon contactwith the printing substrate, the molten ink solidifies rapidly, enablingthe dye to remain on the surface instead of being carried into the paperby capillary action, thereby enabling higher print density than isgenerally obtained with liquid inks. After the phase-change ink isapplied to the substrate, freezing on the substrate resolidifies theink.

In phase-change printing processes, the ink preferably undergoes achange with temperature from a solid state to a liquid state in adesirably short period of time, typically in less than about 100milliseconds. One advantage of phase-change inks is their ability toprint superior images on plain paper, since the phase-change ink quicklysolidifies as it cools, and, since it is primarily waxy in nature, itdoes not normally soak into a paper medium.

Phase-change inks also preferably exhibit a high degree of transparency,generally measured in terms of haze value of the ink. Transparent, lowhaze inks exhibit high gloss and high optical density compared to opaqueinks, although both may appear to be evenly colored.

The use of phase-change inks in acoustic ink printing processes is alsoknown. U.S. Pat. No. 4,745,419 (Quate et al.), the disclosure of whichis totally incorporated herein by reference, discloses acoustic inkprinters of the type having a printhead including one or more acousticdroplet ejectors for supplying focused acoustic beams. The printercomprises a carrier for transporting a generally uniformly thick film ofhot melt ink across its printhead, together with a heating means forliquefying the ink as it nears the printhead. The droplet ejector orejectors are acoustically coupled to the ink via the carrier, and theiroutput focal plane is essentially coplanar with the free surface of theliquefied ink, thereby enabling them to eject individual droplets of inktherefrom on command. The ink, on the other hand, is moved across theprinthead at a sufficiently high rate to maintain the free surface whichit presents to the printhead at a substantially constant level. Avariety of carriers may be employed, including thin plastic and metallicbelts and webs, and the free surface of the ink may be completelyexposed or it may be partially covered by a mesh or perforated layer. Aseparate heating element may be provided for liquefying the ink, or thelower surface of the carrier may be coated with a thin layer ofelectrically resistive material for liquefying the ink by localizedresistive heating.

U.S. Pat. No. 5,541,627 (Quate), the disclosure of which is totallyincorporated herein by reference, discloses a method and apparatus forejecting droplets from the crests of capillary waves riding on the freesurface of a liquid by parametrically pumping the capillary waves withelectric fields from probes located near the crests. Crest stabilizersare beneficially used to fix the spatial locations of the capillary wavecrests near the probes. The probes are beneficially switchably connectedto an AC voltage supply having an output that is synchronized with thecrest motion. When the AC voltage is applied to the probes, theresulting electric field adds sufficient energy to the system so thatthe surface tension of the liquid is overcome and a droplet is ejected.The AC voltage is synchronized such that the droplet is ejected aboutwhen the electric field is near is minimum value. A plurality of dropletejectors are arranged and the AC voltage is switchably applied so thatejected droplets form a predetermined image on a recording surface. Thecapillary waves can be generated on the free surface of the liquid byusing acoustical energy at a level approaching the onset of dropletejection. The liquid used with the invention must also must be attractedby an electric field.

Phase-change inks used in acoustic ink printing processes alsopreferably exhibit a low acoustic-loss value, typically below about 100decibels per millimeter. In addition, the ink vehicle preferably canfill the pores of a porous substrate, such as paper, and preferably hasa melting point of from about 80 to about 120° C.; this melting point,along with low acoustic-loss, enables a minimization of energyconsumption. When the phase-change inks are used in an electric fieldassisted acoustic ink printing process, the inks also are sufficientlyconductive to permit the transmission of electrical signals generated bythe electric field assisted acoustic ink jet printer; the inkspreferably exhibit a conductivity of from about 2 to about 9log(picomho/cm) (measured under melt conditions at about 150° C. byplacing an aluminum electrode in the molten ink and reading theresistivity output on a GenRad 1689 precision RLC Digibridge at afrequency of 1 kiloHertz). In general, the conductivity of a materialcan be measured in terms of the reciprocal of resistivity, which is thecapacity for electrical resistance. Further information regardingelectric field assisted acoustic ink printing processes is disclosed in,for example, Copending Application U.S. Ser. No. 09/280,717, filed Mar.30, 1999, entitled “Method and Apparatus for Moving Ink Drops using anElectric Field and Transfuse Printing System Using the Same,” with thenamed inventors John S. Berkes, Vittorio R. Castelli, Scott A. Elrod,Gregory J. Kovacs, Meng H. Lean, Donald L. Smith, Richard G. Stearns,and Joy Roy, the disclosure of which is totally incorporated herein byreference, which discloses a method of forming and moving ink dropsacross a gap between a printhead and a print medium or intermediateprint medium in a marking device. The method includes generating anelectric field, forming the ink drops adjacent to the printhead, andcontrolling the electric field. The electric field is generated toextend across the gap. The ink drops are formed in an area adjacent tothe printhead. The electric field is controlled such that an electricalattraction force exerted on the formed ink drops by the electric fieldis the greatest force acting on the ink drops. The marking device can beincorporated into a transfuse printing system having an intermediateprint medium made of one or more materials that allow for lateraldissipation of electrical charge from the incident ink drops.

U.S. Pat. No. 5,876,492 (Malhotra et al.), the disclosure of which istotally incorporated herein by reference, discloses an ink comprising(1) a liquid ester vehicle, (2) a solid ester compound, (3) a liquidcrystalline ester compound, (4) a UV absorber, (5) an antioxidant, and(6) a colorant.

U.S. Pat. No. 5,922,117 (Malhotra et al.), the disclosure of which istotally incorporated herein by reference, discloses an ink compositioncomprising (1) a liquid alcohol vehicle, (2) a solid alcohol compound,(3) a quaternary compound, (4) a lightfastness UV absorber, (5) alightfastness antioxidant, and (6) a colorant.

U.S. Pat. No. 5,902,390 (Malhotra et al.), the disclosure of which istotally incorporated herein by reference, discloses an ink comprising(1) a liquid ketone, (2) a solid ketone, (3) a lightfastness UVabsorber, (4) a lightfastness antioxidant, and (5) a colorant.

U.S. Pat. No. 5,931,995 (Malhotra et al.), the disclosure of which istotally incorporated herein by reference, discloses an ink comprising(1) a liquid aldehyde, a liquid acid, or mixtures thereof, (2) a solidadditive aldehyde compound, a solid additive acid compound, or mixturesthereof, (3) a lightfastness UV absorber, (4) a lightfastnessantioxidant, and (5) a colorant.

U.S. Pat. No. 5,958,119, entitled “Hot Melt Ink Compositions,” filedSep. 23, 1997, with the named inventors Shadi L. Malhotra and DanielleC. Boils, the disclosure of which is totally incorporated herein byreference, discloses an ink composition comprising (1) a liquid cyclicvehicle, (2) a cyclic compound, (3) a liquid crystalline nitrilecompound, (4) a lightfastness UV absorber, (5) a lightfastnessantioxidant, and (6) a colorant.

U.S. Pat. No. 6,045,607, entitled “Ink Compositions,” filed Mar. 30,1999, with the named inventors Marcel P. Breton, Shadi L. Malhotra, andRaymond W. Wong, the disclosure of which is totally incorporated hereinby reference, discloses an ink composition containing (1) a first solidcarbamate, (2) a second carbamate with a dissimilar melting point fromthe first solid carbamate (1), (3) a lightfastness component, (4) alightfastness antioxidant, and (5) a colorant.

U.S. Pat. No. 6,123,499, entitled “Inks,” filed Jul. 29, 1999, with thenamed inventors Raymond W. Wong, Marcel P. Breton, Danielle C. Boils,Fatima M. Mayer, and Shadi L. Malhotra, the disclosure of which istotally incorporated herein by reference, discloses an ink compositioncomprising (1) a carbamate or thiourea with a melting point of fromabout 60° C. to about 120° C. and an acoustic-loss value of from about25 to about 80 decibels per millimeter, (2) an alcohol compound with amelting point of about 25° C. to about 90° C. and with an acoustic-lossvalue of from about 5 to about 40 decibels per millimeter, (3) alightfastness component, (4) an antioxidant, and (5) a colorant.

U.S. Pat. No. 6,110,265, entitled “Ink Compositions,” filed Apr. 27,1999, with the named inventors Marcel P. Breton, Shadi L. Malhotra,Raymond W. Wong, Danielle C. Boils, Carl P. Tripp, and Pudupadi R.Sundararajan, the disclosure of which is totally incorporated herein byreference, discloses an ink composition comprising (1) a solid oxazolinecompound with a melting point of from about 60° C. to about 120° C. andan acoustic-loss value of from about 25 to about 80 decibels permillimeter; (2) a carbamate compound with a melting point of from about25° C. to about 100° C.; (3) an alcohol compound; (4) a lightfastnesscomponent; (5) a lightfastness antioxidant; and (6) a colorant.

U.S. Pat. No. 6,096,124, entitled “Ink Compositions,” filed Apr. 27,1999, with the named inventors Raymond W. Wong, Shadi L. Malhotra, andMarcel P. Breton, the disclosure of which is totally incorporated hereinby reference, discloses a conductive ink composition comprising (1) anacid salt; (2) a conductive quaternary compound; (3) a viscositymodifying compound; (4) a lightfastness component; (5) a lightfastnessantioxidant; and (6) a colorant.

U.S. Pat. No. 6,071,333, entitled “Ink Compositions,” filed Apr. 27,1999, with the named inventors Marcel P. Breton, Shadi L. Malhotra, andRaymond W. Wong, the disclosure of which is totally incorporated hereinby reference, discloses an ink composition containing (1) a solidcarbamate compound; (2) an alcohol compound with a melting point of fromabout 25° C. to about 90° C.; (3) a lightfastness component; (4) alightfastness antioxidant; and (5) a colorant.

U.S. Pat. No. 6,086,661, entitled “Ink Compositions,” filed Apr. 27,1999, with the named inventors Shadi L. Malhotra, James D. Mayo, andMarcel P. Breton, the disclosure of which is totally incorporated hereinby reference, discloses an aqueous ink composition comprising (1) aquaternary compound selected from the group consisting of (a)imidazolinium quaternary salts, (b) phosphonium quaternary salts, and(c) ammonium quaternary salts; (2) a liquid ink vehicle; (3) apaper-curl reducing compound; (4) a lightfastness component; (5) alightfastness antioxidant; (6) a substantially water soluble organicsalt or a substantially water soluble inorganic salt; (7) a biocide; and(8) a colorant.

U.S. Pat. No. 6,096,125, entitled “Ink Compositions,” filed Apr. 27,1999, with the named inventors Marcel P. Breton, Shadi L. Malhotra,Danielle C. Boils, Raymond W. Wong, Guerino G. Sacripante, and John M.Lennon, the disclosure of which is totally incorporated herein byreference, discloses an ink composition comprising (1) a mixture of asalt and an oxyalkylene compound wherein the conductive mixturepossesses a melting point of from about 60° C. to about 120° C.; (2) anink vehicle compound with a melting point of from about 80° C. to about100° C.; (3) a viscosity modifying amide compound; (4) a lightfastnesscomponent; (5) a lightfastness antioxidant; and (6) a colorant.

U.S. Pat. No. 6,106,599, entitled “Inks,” filed Jun. 29, 1999, with thenamed inventors Marcel P. Breton, Shadi L. Malhotra, and Raymond W.Wong, the disclosure of which is totally incorporated herein byreference, discloses an ink composition comprising (1) an azolecompound, (2) a viscosity compound, (3) a lightfastness component, (4)an antioxidant, and (5) a colorant.

Copending Application U.S. Ser. No. 09/342,947, entitled “InkCompositions,” filed Jun. 29, 1999, with the named inventors Marcel P.Breton, Shadi L. Malhotra, and Gregory J. Kovacs, the disclosure ofwhich is totally incorporated herein by reference, discloses an inkcomposition comprising (1) a polymer; (2) an acid compound of theformula CH₃(CH₂)_(m)(CH₂CH═CH)_(p)(CH₂)_(n)COOH wherein n, m, and prepresent the number of segments; (3) a conductive component; (4) alightfastness component; and (5) a colorant.

Copending Application U.S. Ser. No. 09/281,682, entitled “InkCompositions,” filed Mar. 30, 1999, with the named inventors H. BruceGoodbrand, Danielle C. Boils, Pudupadi R. Sundararajan, Raymond W. Wong,and Shadi L. Malhotra, the disclosure of which is totally incorporatedherein by reference, discloses an ink composition comprising (1) athiourea with a melting point of from about 60 to about 120° C. and withan acoustic-loss value of from about 25 to about 80 decibels permillimeter, (2) an optional ink carbamate with a melting point of fromabout 25° C. to about 60° C. and with an acoustic-loss value of fromabout 5 to about 40 decibels per millimeter, (3) a lightfastnesscomponent, (4) a lightfast antioxidant, and (5) a colorant.

U.S. Pat. No. 6,066,200, entitled “Ink Compositions,” filed Apr. 27,1999, with the named inventors Marcel P. Breton, Shadi L. Malhotra, andRaymond W. Wong, the disclosure of which is totally incorporated hereinby reference, discloses an ink composition comprising (1) a solid ureacompound; (2) an alcohol; (3) a lightfastness component; (4) a lightfastantioxidant; and (5) a colorant.

U.S. Pat. No. 6,106,601, entitled “Ink Compositions,” filed Apr. 27,1999, with the named inventors Shadi L. Malhotra, Raymond W. Wong, andMarcel P. Breton, the disclosure of which is totally incorporated hereinby reference, discloses an ink composition comprising (1) an oxazolinecompound; (2) a thiourea compound with an optional melting point of fromabout 25 to about 100° C. and with an optional acoustic-loss value offrom about 5 to about 40 decibels per millimeter; (3) an alcohol; (4) alightfastness compound; (5) an antioxidant; and (6) a colorant.

Copending Application U.S. Ser. No. 09/401,249, entitled “ConductiveInks Containing Sulfonate Salts,” filed concurrently herewith, with thenamed inventors Shadi L. Malhotra, Raymond W. Wong, and Marcel P.Breton, the disclosure of which is totally incorporated herein byreference, discloses an ink composition comprising (a) an ink vehiclewhich is selected from (i) 1,3-dialkyl ureas, (ii) N,N′-ethylenebisalkylamides, (iii)N-[4-chloro-3-[4,5-dihydro-5-oxo-1-(2,4,6-trichlorophenyl)-1H-pyrazol-3-ylamino]phenyl]-2-(1-octadecenyl)succinimide,(iv) 1,3-diamino-5,6-bis(octyloxy)isoindoline, (v) N,N-dimethylalkylamine N-oxides, (vi) alkyl amides, or (vii) mixtures thereof, saidink vehicle having a melting point of no lower than about 60° C. and nohigher than about 155° C., (b) a viscosity modifier which is an amidehaving a melting point of no lower than about 60° C. and no higher thanabout 155° C., (c) a conductive sulfonate salt having a melting point ofno lower than about 60° C. and no higher than about 155° C., (d) acolorant, (e) an optional antioxidant, and (f) an optional ultravioletabsorber.

U.S. Pat. No. 6,113,678, entitled “Hot Melt Inks ContainingPolyanhydrides,” filed concurrently herewith, with the named inventorShadi L. Malhotra, the disclosure of which is totally incorporatedherein by reference, discloses an ink composition comprising (a) apolyanhydride ink vehicle, (b) a nonpolymeric anhydride viscositymodifier, and (c) a colorant.

Copending Application U.S. Ser. No. 09/404,570, entitled “Hot Melt InksContaining Aldehyde Copolymers,” filed concurrently herewith, with thenamed inventor Shadi L. Malhotra, the disclosure of which is totallyincorporated herein by reference, discloses an ink compositioncomprising (a) an aldehyde copolymer ink vehicle, (b) a nonpolymericaldehyde viscosity modifier, (c) a colorant, (d) an optionalconductivity enhancing agent, (e) an optional antioxidant, and (f) anoptional UV absorber.

Copending Application U.S. Ser. No. 09/401,740, entitled “Hot Melt InksContaining Styrene or Terpene Polymers,” filed concurrently herewith,with the named inventor Shadi L. Malhotra, the disclosure of which istotally incorporated herein by reference, discloses an ink compositioncomprising (a) a styrene polymer or terpene polymer hardening component,(b) a nonpolymeric aromatic viscosity modifier, (c) a colorant, (d) anoptional nonpolymeric aromatic ink vehicle, (e) an optional colorantdispersing agent, (f) an optional conductivity enhancing agent, (g) anoptional antioxidant, and (h) an optional UV absorber.

U.S. Pat. No. 6,117,223, entitled “Hot Melt Inks ContainingPolyketones,” filed concurrently herewith, with the named inventor ShadiL. Malhotra, the disclosure of which is totally incorporated herein byreference, discloses an ink composition comprising (a) a nonpolymericketone ink vehicle having a melting point of at least about 60° C., (b)a polyketone hardening component, (c) a colorant, (d) a conductivityenhancing agent, (e) an optional antioxidant, (f) an optional viscositymodifier which is a nonpolymeric carbonate, monoketone, or diketone, and(g) an optional ultraviolet absorber.

Copending Application U.S. Ser. No. 09/401,250, entitled “Hot Melt InksContaining Polyesters,” filed concurrently herewith, with the namedinventor Shadi L. Malhotra, the disclosure of which is totallyincorporated herein by reference, discloses an ink compositioncomprising (a) a polyester ink vehicle, (b) a nonpolymeric esterviscosity modifier, (c) a colorant, (d) an optional colorant dispersingagent, (e) an optional conductivity enhancing agent, (f) an optionalantioxidant, and (g) an optional UV absorber.

While known compositions and processes are suitable for their intendedpurposes, a need remains for improved phase-change inks. In addition, aneed remains for improved inks for acoustic ink printing. Further, aneed remains for conductive inks. Additionally, a need remains forphase-change inks with desirable melting point values. There is also aneed for phase-change inks with melt viscosities at jetting temperaturesthat enable high quality ink jet printing. In addition, there is a needfor phase-change inks that generate images with excellent hardnessvalues. Further, there is a need for phase-change inks undergo, uponheating, a change from a solid state to a liquid state in a desirablyrapid period of time. Additionally, there is a need for phase-changeinks with acoustic-loss values that are desirable for acoustic inkprinting applications. A need also remains for phase-change inkcompositions with conductivity values that are desirable for electricfield assisted acoustic ink printing processes. In addition, a needremains for phase-change inks that generate images with desirably lowhaze values. Further, a need remains for phase-change inks that generateimages with good crease resistance. Additionally, a need remains forphase-change inks that generate images with high gloss.

SUMMARY OF THE INVENTION

The present invention is directed to an ink composition comprising (a)an ink vehicle which comprises a conductive pyridinium compound having amelting point of no lower than about 60° C. and no higher than about155° C., (b) a viscosity modifier which is a pyridine compound, apyrimidine compound, a pyrazine compound, a pyridazine compound, ormixtures thereof, said pyridine, pyrimidine, pyrazine, or pyridazinecompounds having a melting point of no lower than about 60° C. and nohigher than about 155° C., (c) a binder which is a polymeric pyridine orpyridinium compound; (d) a colorant, (e) an optional antioxidant, and(f) an optional UV absorber.

DETAILED DESCRIPTION OF THE INVENTION

The ink compositions of the present invention contain an ink vehicle.This ink vehicle is a conductive nonpolymeric pyridinium compound, andis a solid at ambient temperature (typically from about 20 to about 25°C., although ambient temperature can be outside of these ranges).Suitable pyridinium compounds include those of the general formula

wherein each of R₁, R₂, R₃, R₄, R₅, and R₆, independently of the others,can be (but are not limited to) hydrogen atoms, alkyl and alkoxy groups,including saturated, unsaturated, branched, linear, and cyclic alkyl andalkoxy groups (typically with from 1 to about 30 carbon atoms, althoughthe number of carbon atoms can be outside of this range), includingsubstituted and unsubstituted alkyl and alkoxy groups, aryl and aryloxygroups (typically with from 6 to about 30 carbon atoms, although thenumber of carbon atoms can be outside of this range), includingsubstituted and unsubstituted aryl and aryloxy groups, arylalkyl,arylalkyloxy, alkylaryl, and alkylaryloxy groups (typically with from 7to about 30 carbon atoms, although the number of carbon atoms can beoutside of this range), including substituted and unsubstitutedarylalkyl, arylalkyloxy, alkylaryl, and alkylaryloxy groups,heterocyclic groups (typically with from about 5 to about 10 ring atoms,wherein the hetero atoms can be (but are not limited to) oxygen atoms,nitrogen atoms, sulfur atoms, phosphorus atoms, silicon atoms, and thelike), including substituted and unsubstituted heterocyclic groups,hydroxy groups, amine groups, imine groups, ammonium groups, pyridinegroups, pyridinium groups, ether groups, ester groups, amide groups,carbonyl groups, thiocarbonyl groups, sulfate groups, sulfonate groups,sulfide groups, sulfoxide groups, phosphine groups, phosphonium groups,phosphate groups, mercapto groups, nitroso groups, sulfone groups, acylgroups, acid anhydride groups, azide groups, and the like, wherein twoor more substituents can be joined together to form a ring, wherein thesubstituents on the substituted alkyl, alkoxy, aryl, aryloxy, arylalkyl,arylalkyloxy, alkylaryl, alkylaryloxy, and heterocyclic groups can be(but are not limited to) hydroxy groups, amine groups, imine groups,ammonium groups, pyridine groups, pyridinium groups, ether groups, estergroups, amide groups, carbonyl groups, thiocarbonyl groups, sulfategroups, sulfonate groups, sulfide groups, sulfoxide groups, phosphinegroups, phosphonium groups, phosphate groups, mercapto groups, nitrosogroups, sulfone groups, acyl groups, acid anhydride groups, azidegroups, and the like, A is any desired or suitable anion, with examplesof anions including (but not limited to) Cl⁻, Br⁻, I⁻, HSO₄ ⁻, HSO₃ ⁻,SO₄ ²⁻, SO₃ ²⁻, CH₂SO₃ ⁻, CH₃SO₃ ⁻, CH₃C₆H₄SO₃ ⁻, NO₃ ⁻, HCOO⁻, CH₃COO⁻,HCO₃ ⁻, CO₃ ²⁻, H₂PO₄ ⁻, HPO₄ ²⁻, PO₄ ³⁻, SCN⁻, BF₄ ⁻, ClO₄ ⁻, SSO₃ ⁻,and the like, as well as mixtures thereof, and n is an integer; ntypically is 1, 2, or 3, but when the anion is polymeric, the value of nis not limited. Examples of suitable conductive pyridinium compoundsinclude (1) 1-propyl pyridinium salts, such as 1-propyl pyridiniumbromide (Aldrich 41,288-0), of the formula

(2) 1-ethyl-3-hydroxy pyridinium salts, such as 1-ethyl-3-hydroxypyridinium bromide (Aldrich 19,264-3), of the formula

(3) 1-ethyl-4-phenyl pyridinium salts, such as 1-ethyl-4-phenylpyridinium iodide (Aldrich 36,208-5), of the formula

(4) 1-ethyl-4-(methoxy carbonyl) pyridinium salts, such as1-ethyl-4-(methoxy carbonyl) pyridinium iodide (Aldrich 32,625-9), ofthe formula

(5) pyridinium 3-nitrobenzene sulfonate (Aldrich 27,198-5), of theformula

(6) pyridinium-ρ-toluene sulfonate (Aldrich 23,223-8), (7) pyridiniumtrifluoroacetate (Aldrich 21,513-9), (8) 1-heptyl-4-(4-pyridyl)pyridinium salts, such as 1-heptyl-4-(4-pyridyl) pyridinium bromide(Aldrich 37,778-3), of the formula

(9) cetyl pyridinium salts, such as cetyl pyridinium bromide monohydrate(Aldrich 28,531-5), of the formula

and cetyl pyridinium chloride monohydrate (Aldrich 85,556-1), (10)1-dodecyl pyridinium salts, such as 1-dodecyl pyridinium chloridehydrate (Aldrich 27,860-2), of the formula

and the like, as well as mixtures thereof. The conductive pyridinium inkvehicle is present in the ink in any desired or effective amount,typically no less than about 0.5 percent by weight of the ink,preferably no less than about 10 percent by weight of the ink, and morepreferably no less than about 25 percent by weight of the ink, andtypically no more than about 98 percent by weight of the ink, preferablyno more than about 80 percent by weight of the ink, more preferably nomore than about 75 percent by weight of the ink, and even morepreferably no more than about 60 percent by weight of the ink, althoughthe amount can be outside of these ranges. Preferably, the ink vehiclehas a melting point of from about 60 to about 155° C. and anacoustic-loss value of no more than about 100 decibels per millimeter,although the melting point and acoustic-loss value can be outside ofthese ranges. In addition, conductive materials generally are preferredto nonconductive materials, although nonconductive materials can also beemployed.

The ink compositions of the present invention also contain a viscositymodifier. The viscosity modifier is a nonpolymeric pyridine compound, anonpolymeric pyrimidine compound, a nonpolymeric pyrazine compound, anonpolymeric pyridazine compound, or a mixture thereof. Pyridinecompounds include those of the general formula

wherein each of R₁, R₂, R₃, R₄, and R₅, independently of the others, canbe (but are not limited to) hydrogen atoms, alkyl and alkoxy groups,including saturated, unsaturated, branched, linear, and cyclic alkyl andalkoxy groups (typically with from 1 to about 30 carbon atoms, althoughthe number of carbon atoms can be outside of this range), includingsubstituted and unsubstituted alkyl and alkoxy groups, aryl and aryloxygroups (typically with from 6 to about 30 carbon atoms, although thenumber of carbon atoms can be outside of this range), includingsubstituted and unsubstituted aryl and aryloxy groups, arylalkyl,arylalkyloxy, alkylaryl, and alkylaryloxy groups (typically with from 7to about 30 carbon atoms, although the number of carbon atoms can beoutside of this range), including substituted and unsubstitutedarylalkyl, arylalkyloxy, alkylaryl, and alkylaryloxy groups,heterocyclic groups (typically with from about 5 to about 10 ring atoms,wherein the hetero atoms can be (but are not limited to) oxygen atoms,nitrogen atoms, sulfur atoms, phosphorus atoms, silicon atoms, and thelike), including substituted and unsubstituted heterocyclic groups,hydroxy groups, amine groups, imine groups, ammonium groups, pyridinegroups, pyridinium groups, ether groups, ester groups, amide groups,carbonyl groups, thiocarbonyl groups, sulfate groups, sulfonate groups,sulfide groups, sulfoxide groups, phosphine groups, phosphonium groups,phosphate groups, mercapto groups, nitroso groups, sulfone groups, acylgroups, acid anhydride groups, azide groups, and the like, wherein twoor more substituents can be joined together to form a ring, wherein thesubstituents on the substituted alkyl, alkoxy, aryl, aryloxy, arylalkyl,arylalkyloxy, alkylaryl, alkylaryloxy, and heterocyclic groups can be(but are not limited to) hydroxy groups, amine groups, imine groups,ammonium groups, pyridine groups, pyridinium groups, ether groups, estergroups, amide groups, carbonyl groups, thiocarbonyl groups, sulfategroups, sulfonate groups, sulfide groups, sulfoxide groups, phosphinegroups, phosphonium groups, phosphate groups, mercapto groups, nitrosogroups, sulfone groups, acyl groups, acid anhydride groups, azidegroups, and the like. Specific examples of suitable pyridine compoundsinclude (1) 2-hydroxy pyridine (Aldrich H5,680-1), (2) 3-hydroxypyridine (Aldrich H5,700-9), (3) 2-pyridine carboxamide (Aldrich10,405-1), (4) syn-2-pyridine aldoxime (Aldrich P5,820-0), of theformula

(5) 4,4′-dipyridyl (also known as 4,4′-bipyridine) (Aldrich 28,942-6),(6) 2,2′-dipyridyl amine (Aldrich D21,630-5), (7) 4,4′-dipyridyldisulfide (Aldrich 14,305-7), (8) 1,2-bis(4-pyridyl)ethane (AldrichB5,180-1), (9) 1,2-bis(4-pyridyl) ethylene (Aldrich B5,260-3), (10)3-amino-2-chloropyridine (Aldrich A4,690-0), (11)5-amino-2-chloropyridine (Aldrich 18,877-8), (12) 2,3-diaminopyridine(Aldrich 12,585-7), (13) 2,6-diaminopyridine (Aldrich 17,950-7), (14)2,5-dibromopyridine (Aldrich D4,310-7), (15) 3,5-dibromopyridine(Aldrich 12,016-2), (16) 2,6-dibromopyridine (Aldrich D4,311-5), (17)2,6-dichloropyridine (Aldrich D7,370-7), (18) 2-benzyl aminopyridine(Aldrich 19,505-7), (19) 3,4-dipyridine dicarbonitrile (Aldrich31,023-9), of the formula

(20) 2,6-pyridine dicarboxaldehyde (Aldrich 25,600-5), of the formula

(21) 3,4-pyridine dicarboxylic anhydride (Aldrich 28,271-5), (22)2,6-pyridine dimethanol (Aldrich 15,436-9), (23)3-hydroxy-2-nitropyridine (Aldrich 10,725-5), (24)2-methoxy-5-nitropyridine (Aldrich M1,820-5), (25) dimethyl 2,6-pyridinedicarboxylate (Aldrich 37,933-6), (26) 2-amino-3,5-dichloropyridine(Aldrich 13,592-5), (27) 2-amino-3,5-dibromopyridine (Aldrich 18,050-5),(28) 2-(2-aminoethyl amino)-5-nitropyridine (Aldrich 11,346-8), (29)2,6-bis(chloromethyl) pyridine (Aldrich 40,541-8), (30)2-chloro-6-methoxy-3-nitropyridine (Aldrich C4,990-9), (31)2-chloro-6-methyl-3-pyridine carbonitrile (Aldrich 36,257-3), (32)3,5-diacetyl-2,6-dimethylpyridine (Aldrich 39,278-2), (33) diethyl(6-methyl-2-pyridyl amino methylene) malonate (Aldrich 38,037-7), (34)3-hydroxy-6-methyl-2-nitropyridine (Aldrich 23,274-2), (35)1-(2-pyridyl)-2-(4-pyridyl) ethylene (Aldrich 19,745-9), (36)1-acetyl-1H-1,2,3-triazolo-[4,5-b] pyridine (Aldrich 34,727-2), (37)di-2-pyridyl thionocarbonate (Aldrich 31,102-2), and the like, as wellas mixtures thereof. Suitable pyrimidine compounds include those of thegeneral formula

wherein each of R₁, R₂, R₃, and R₄, independently of the others, can be(but are not limited to) hydrogen atoms, alkyl and alkoxy groups,including saturated, unsaturated, branched, linear, and cyclic alkyl andalkoxy groups (typically with from 1 to about 30 carbon atoms, althoughthe number of carbon atoms can be outside of this range), includingsubstituted and unsubstituted alkyl and alkoxy groups, aryl and aryloxygroups (typically with from 6 to about 30 carbon atoms, although thenumber of carbon atoms can be outside of this range), includingsubstituted and unsubstituted aryl and aryloxy groups, arylalkyl,arylalkyloxy, alkylaryl, and alkylaryloxy groups (typically with from 7to about 30 carbon atoms, although the number of carbon atoms can beoutside of this range), including substituted and unsubstitutedarylalkyl, arylalkyloxy, alkylaryl, and alkylaryloxy groups,heterocyclic groups (typically with from about 5 to about 10 ring atoms,wherein the hetero atoms can be (but are not limited to) oxygen atoms,nitrogen atoms, sulfur atoms, phosphorus atoms, silicon atoms, and thelike), including substituted and unsubstituted heterocyclic groups,hydroxy groups, amine groups, imine groups, ammonium groups, pyridinegroups, pyridinium groups, ether groups, ester groups, amide groups,carbonyl groups, thiocarbonyl groups, sulfate groups, sulfonate groups,sulfide groups, sulfoxide groups, phosphine groups, phosphonium groups,phosphate groups, mercapto groups, nitroso groups, sulfone groups, acylgroups, acid anhydride groups, azide groups, and the like, wherein twoor more substituents can be joined together to form a ring, wherein thesubstituents on the substituted alkyl, alkoxy, aryl, aryloxy, arylalkyl,arylalkyloxy, alkylaryl, alkylaryloxy, and heterocyclic groups can be(but are not limited to) hydroxy groups, amine groups, imine groups,ammonium groups, pyridine groups, pyridinium groups, ether groups, estergroups, amide groups, carbonyl groups, thiocarbonyl groups, sulfategroups, sulfonate groups, sulfide groups, sulfoxide groups, phosphinegroups, phosphonium groups, phosphate groups, mercapto groups, nitrosogroups, sulfone groups, acyl groups, acid anhydride groups, azidegroups, and the like. Specific examples of suitable pyrimidine compoundsinclude (1) 2-aminopyrimidine (Aldrich A7,860-8), (2)2-amino-4,6-dimethoxypyrimidine (Aldrich 37,534-9), (3)6-chloro-2,4-dimethoxypyrimidine (Aldrich C3,640-8), (4)4,6-dichloro-2-methylthio-5-phenylpyrimidine (Aldrich 14,419-3), (5)4,6-dichloro-5-nitropyrimidine (Aldrich D6,930-0), and the like as wellas mixtures thereof. Examples of suitable pyrazine and pyridazinecompounds include those of the general formulae

respectively, wherein each of R₁, R₂, R₃, and R₄, independently of theothers, can be (but are not limited to) hydrogen atoms, alkyl and alkoxygroups, including saturated, unsaturated, branched, linear, and cyclicalkyl and alkoxy groups (typically with from 1 to about 30 carbon atoms,although the number of carbon atoms can be outside of this range),including substituted and unsubstituted alkyl and alkoxy groups, aryland aryloxy groups (typically with from 6 to about 30 carbon atoms,although the number of carbon atoms can be outside of this range),including substituted and unsubstituted aryl and aryloxy groups,arylalkyl, arylalkyloxy, alkylaryl, and alkylaryloxy groups (typicallywith from 7 to about 30 carbon atoms, although the number of carbonatoms can be outside of this range), including substituted andunsubstituted arylalkyl, arylalkyloxy, alkylaryl, and alkylaryloxygroups, heterocyclic groups (typically with from about 5 to about 10ring atoms, wherein the hetero atoms can be (but are not limited to)oxygen atoms, nitrogen atoms, sulfur atoms, phosphorus atoms, siliconatoms, and the like), including substituted and unsubstitutedheterocyclic groups, hydroxy groups, amine groups, imine groups,ammonium groups, pyridine groups, pyridinium groups, ether groups, estergroups, amide groups, carbonyl groups, thiocarbonyl groups, sulfategroups, sulfonate groups, sulfide groups, sulfoxide groups, phosphinegroups, phosphonium groups, phosphate groups, mercapto groups, nitrosogroups, sulfone groups, acyl groups, acid anhydride groups, azidegroups, and the like, wherein two or more substituents can be joinedtogether to form a ring, wherein the substituents on the substitutedalkyl, alkoxy, aryl, aryloxy, arylalkyl, arylalkyloxy, alkylaryl,alkylaryloxy, and heterocyclic groups can be (but are not limited to)hydroxy groups, amine groups, imine groups, ammonium groups, pyridinegroups, pyridinium groups, ether groups, ester groups, amide groups,carbonyl groups, thiocarbonyl groups, sulfate groups, sulfonate groups,sulfide groups, sulfoxide groups, phosphine groups, phosphonium groups,phosphate groups, mercapto groups, nitroso groups, sulfone groups, acylgroups, acid anhydride groups, azide groups, and the like. Specificexamples of suitable pyrazine and pyridazine compounds include (1) aminopyrazine (Aldrich A7,695-8), (2) 3-chloro-6-methoxypyridazine (Aldrich10,859-6), (3) 3,6-dichloro-4-methylpyridazine (Aldrich 29,774-7), (4)2,3-dimethylquinoxaline (Aldrich D18,497-7), of the formula

and the like, as well as mixtures thereof. The viscosity modifiergenerally acts to lower the viscosity of the ink at the jettingtemperature, typically lowering the viscosity by from about 10 to about20 centipoise compared to a similar composition containing no viscositymodifier, although the quantitative viscosity adjustment can be outsideof this range. The viscosity modifier is present in the ink in anydesired or effective amount, typically no less than about 1 percent byweight of the ink, preferably no less than about 20 percent by weight ofthe ink, and more preferably no less than about 30 percent by weight ofthe ink, and typically no more than about 98 percent by weight of theink, preferably no more than about 70 percent by weight of the ink, morepreferably no more than about 50 percent by weight of the ink, and evenmore preferably no more than about 40 percent by weight of the ink,although the amount can be outside of these ranges. Preferably, theviscosity modifier has a melting point of from about 60 to about 155° C.and an acoustic-loss value of no more than about 100 decibels permillimeter, although the melting point and acoustic-loss value can beoutside of these ranges. In addition, conductive materials generally arepreferred to nonconductive materials, although nonconductive materialscan also be employed.

The ink compositions of the present invention further contain a binderwhich is a polymeric pyridine or pyridinium compound. Both homopolymersof pyridine or pyridinium monomers and copolymers (including random,alternating, block, and graft copolymers) of pyridine or pyridiniummonomers and other monomers are suitable. Specific examples of suitablepolymeric pyridine and pyridinium compounds include (1) poly(4-vinylpyridinium-ρ-toluene sulfonate) (Aldrich 36,273-5), of the formula

(2) poly(4-vinyl pyridinium tribromide) (Aldrich 36,272-7), of theformula

(3) poly(4-vinyl pyridinium polyhydrogen fluoride) (Carus ChemicalCompany), (4) poly(4-vinyl pyridinium-co-butyl methacrylate) (50 percentby weight butyl methacrylate; Scientific Polymer Products; Aldrich30,625-8), of the formula

(5) polyvinyl pyridine (Reilly Industries Incorporated), of the formula

and the like, as well as mixtures thereof. The polymeric pyridiniumbinder is present in the ink in any desired or effective amount,typically no less than about 0.5 percent by weight of the ink, andpreferably no less than about 5 percent by weight of the ink, andtypically no more than about 98 percent by weight of the ink, preferablyno more than about 18 percent by weight of the ink, more preferably nomore than about 15 percent by weight of the ink, and even morepreferably no more than about 10 percent by weight of the ink, althoughthe amount can be outside of these ranges.

Any desired or effective colorant can be employed in the inks of thepresent invention, including dyes, pigments, mixtures thereof, and thelike, provided that the colorant can be dissolved or dispersed in theink vehicle, with spirit soluble dyes being preferred. The colorant ispresent in the ink in any desired or effective amount to obtain thedesired color and hue, typically no less than about 0.5 percent byweight of the ink, and preferably no less than about 3 percent by weightof the ink, and typically no more than about 20 percent by weight of theink, and preferably no more than about 12 percent by weight of the ink,although the amount can be outside of these ranges.

Examples of suitable pigments include Violet Toner VT-8015 (PaulUhlich); Paliogen Violet 5100 (BASF); Paliogen Violet 5890 (BASF);Permanent Violet VT 2645 (Paul Uhlich); Heliogen Green L8730 (BASF);Argyle Green XP-111-S (Paul Uhlich); Brilliant Green Toner GR 0991 (PaulUhlich); Lithol Scarlet D3700 (BASF); Toluidine Red (Aldrich); Scarletfor Thermoplast NSD PS PA (Ugine Kuhlmann of Canada); E. D. ToluidineRed (Aldrich); Lithol Rubine Toner (Paul Uhlich); Lithol Scarlet 4440(BASF); Bon Red C (Dominion Color Company); Royal Brilliant Red RD-8192(Paul Uhlich); Oracet Pink RF (Ciba-Geigy); Paliogen Red 3871K (BASF);Paliogen Red 3340 (BASF); Lithol Fast Scarlet L4300 (BASF); HeliogenBlue L6900, L7020 (BASF); Heliogen Blue K6902, K6910 (BASF); HeliogenBlue D6840, D7080 (BASF); Sudan Blue OS (BASF); Neopen Blue FF4012(BASF); PV Fast Blue B2G01 (American Hoechst); Irgalite Blue BCA(Ciba-Geigy); Paliogen Blue 6470 (BASF); Sudan III (Red Orange)(Matheson, Colemen Bell); Sudan II (Orange) (Matheson, Colemen Bell);Sudan Orange G (Aldrich), Sudan Orange 220 (BASF); Paliogen Orange 3040(BASF); Ortho Orange OR 2673 (Paul Uhlich); Paliogen Yellow 152, 1560(BASF); Lithol Fast Yellow 0991K (BASF); Paliotol Yellow 1840 (BASF);Novoperm Yellow FGL (Hoechst); Permanent Yellow YE 0305 (Paul Uhlich);Lumogen Yellow D0790 (BASF); Suco-Yellow L1250 (BASF); Suco-Yellow D1355(BASF); Suco Fast Yellow D1355, D1351 (BASF); Hostaperm Pink E (AmericanHoechst); Fanal Pink D4830 (BASF); Cinquasia Magenta (Du Pont); PaliogenBlack L0084 (BASF); Pigment Black K801 (BASF); and carbon blacks such asREGAL 330® (Cabot), Carbon Black 5250, Carbon Black 5750 (ColumbiaChemical), and the like.

Examples of suitable dyes include Pontamine; Food Black 2; CarodirectTurquoise FBL Supra Conc. (Direct Blue 199), available from CarolinaColor and Chemical; Special Fast Turquoise 8 GL Liquid (Direct Blue 86),available from Mobay Chemical; Intrabond Liquid Turquoise GLL (DirectBlue 86), available from Crompton and Knowles; Cibracron Brilliant Red38-A (Reactive Red 4), available from Aldrich Chemical; DrimareneBrilliant Red X-2B (Reactive Red 56), available from Pylam, Inc.;Levafix Brilliant Red E-4B, available from Mobay Chemical; LevafixBrilliant Red E6-BA, available from Mobay Chemical; Procion Red H8B(Reactive Red 31), available from ICI America; Pylam Certified D&C Red#28 (Acid Red 92), available from Pylam; Direct Brill Pink B GroundCrude, available from Crompton and Knowles; Cartasol Yellow GTFPresscake, available from Sandoz, Inc.; Tartrazine Extra Conc. (FD&CYellow #5, Acid Yellow 23), available from Sandoz, Inc.; CarodirectYellow RL (Direct Yellow 86), available from Carolina Color andChemical; Cartasol Yellow GTF Liquid Special 110, available from Sandoz,Inc.; D&C Yellow #10 (Acid Yellow 3), available from Tricon; YellowShade 16948, available from Tricon; Basacid Black X 34, available fromBASF; Carta Black 2GT, available from Sandoz, Inc.; and the like.Particularly preferred are solvent dyes; within the class of solventdyes, spirit soluble dyes are preferred because of their compatibilitywith the ink vehicles of the present invention. Examples of suitablespirit solvent dyes include Neozapon Red 492 (BASF); Orasol Red G(Ciba-Geigy); Direct Brilliant Pink B (Crompton & Knowles); Aizen SpilonRed C-BH (Hodogaya Chemical); Kayanol Red 3BL (Nippon Kayaku); LevanolBrilliant Red 3BW (Mobay Chemical); Levaderm Lemon Yellow (MobayChemical); Spirit Fast Yellow 3G; Aizen Spilon Yellow C-GNH (HodogayaChemical); Sirius Supra Yellow GD 167; Cartasol Brilliant Yellow 4GF(Sandoz); Pergasol Yellow CGP (Ciba-Geigy); Orasol Black RLP(Ciba-Geigy); Savinyl Black RLS (Sandoz); Dermacarbon 2GT (Sandoz);Pyrazol Black BG (ICI); Morfast Black Conc. A (Morton-Thiokol); DiaazolBlack RN Quad (ICI); Orasol Blue GN (Ciba-Geigy); Savinyl Blue GLS(Sandoz); Luxol Blue MBSN (Morton-Thiokol); Sevron Blue 5GMF (ICI);Basacid Blue 750 (BASF), and the like. Neozapon Black X51 [C.I. SolventBlack, C.I. 12195] (BASF), Sudan Blue 670 [C.I. 61554] (BASF), SudanYellow 146 [C.I. 12700] (BASF), and Sudan Red 462 [C.I. 26050] (BASF)are preferred.

The optional antioxidants of the ink compositions protect the imagesfrom oxidation and also protect the ink components from oxidation duringthe heating portion of the ink preparation process. Specific examples ofsuitable antioxidants include (but are not limited to) (1)2,6-di-tert-butyl-4-methoxyphenol (Aldrich 25,106-2), (2)2,4-di-tert-butyl-6-(4-methoxybenzyl) phenol (Aldrich 23,008-1), (3)4-bromo-2,6-dimethylphenol (Aldrich 34,951-8), (4)4-bromo-3,5-didimethylphenol (Aldrich B6,420-2), (5)4-bromo-2-nitrophenol (Aldrich 30,987-7), (6) 4-(diethylaminomethyl)-2,5-dimethylphenol (Aldrich 14,668-4), (7)3-dimethylaminophenol (Aldrich D14,400-2), (8) 2-amino-4-tert-amylphenol(Aldrich 41,258-9), (9) 2,6-bis(hydroxymethyl)-p-cresol (Aldrich22,752-8), (10) 2,2′-methylenediphenol (Aldrich B4,680-8), (11)5-diethylamino)-2-nitrosophenol (Aldrich 26,951-4), (12) antimonydialkyl phosphorodithioate (commercially available from Vanderbilt),(13) molybdenum oxysulfide dithiocarbamate (commercially available fromVanderbilt), (14) (nickel-bis(o-ethyl(3,5-di-tert-butyl-4-hydroxybenzyl)phosphonate (commercially available from Ciba Geigy), (15)4,4′-methylene-bis(dibutyldithiocarbamate) (commercially available asVanlube 7723 from Vanderbilt), (16)tetrasodium-N-(1,2-dicarboxyethyl)-N-octadecyl sulfosuccinamate(commercially available from American Cyanamid), (17)2,6-di-tert-butyl-α-dimethylamino-4-cresol (commercially available asEthanox-703 from Ethyl Corporation), (18)2,2′-isobutylidene-bis(4,6-dimethyl phenol) (commercially available asVulkanox NKF from Mobay Chemicals), (19)2,2′-methylenebis(6-tert-butyl-4-methylphenol) (commercially availableas Cyanox-2246, Aldrich 41,315-5), (20)2,2′-methylenebis(6-tert-butyl-4-ethylphenol) (commercially available asCyanox-425, Aldrich 41,314-3), (21) N-isopropyl-N′-phenyl-phenylenediamine (commercially available as Santoflex-IP from Monsanto Chemicals,(22) N-(1,3-dimethylbutyl)-N′-phenyl-phenylene-diamine (commerciallyavailable as Santoflex-13 from Monsanto Chemicals), (23)N,N′-di(2-octyl)-4-phenylene diamine (commercially available asAntozite-1 from Vanderbilt), (24)N,N′-bis(1,4-dimethylpentyl)-4-phenylene diamine (commercially availableas Santoflex-77 from Monsanto Chemicals), (25)2,4,6-tris-(N-1,4-dimethyl pentyl-4-phenylenediamino)-1,3,5-triazine(commercially available as Durazone-37 from Uniroyal), (26) D-raffinosepentahydrate (Aldrich 20,667-9), (27) 2,2′-methylenebis(6-tert-butyl-4-methyl-phenol) (Aldrich 41,313-5), (28)2,6-di-tert-butyl-4-(dimethylaminomethyl) phenol (Aldrich 41,327-5),(29) 4-dodecylresorcinol (Aldrich D22,260-7), and the like, as well asmixtures thereof. When present, the optional antioxidants are present inany desired or effective amount, typically no less than about 0.25percent by weight of the ink, and preferably no less than about 1percent by weight of the ink, and typically no more than about 98percent by weight of the ink, preferably no more than about 10 percentby weight of the ink, and more preferably no more than about 5 percentby weight of the ink, although the amount can be outside of theseranges.

The optional UV absorbers in the inks of the present invention primarilyprotect the images generated therewith from UV degradation. Specificexamples of suitable UV absorbers include (but are not limited to) (1)2-amino-2′,5-dichlorobenzophenone (Aldrich 10,515-5), (2)2′amino-4′,5′-dimethoxyacetophenone (Aldrich 32,922-3), (3)2-benzyl-2-(dimethylamino)-4′-morpholino butyrophenone (Aldrich40,564-7), (4) 4′-benzyloxy-2′-hydroxy-3′-methylacetophenone (Aldrich29,884-0), (5) 4,4′-bis(diethylamino) benzophenone (Aldrich 16,032-6),(6) 5-chloro-2-hydroxy benzophenone (Aldrich C4,470-2), (7)4′-piperazinoacetophenone (Aldrich 13,646-8), (8)4′-piperidinoacetophenone (Aldrich 11,972-5), (9)2-amino-5-chlorobenzophenone (Aldrich A4,556-4), (10)2-bromo-2′,4-dimethoxyacetophenone (Aldrich 19,948-6), (11)2-bromo-2′,5′-dimethoxyacetophenone (Aldrich 10,458-2), (12)2-bromo-3′-nitroacetophenone (Aldrich 34,421-4), (13)2-bromo-4′-nitroacetophenone (Aldrich 24,561-5), (14)3′,5′-diacetoxyacetophenone (Aldrich 11,738-2, (15) 2-phenylsulfonyl)acetophenone (Aldrich 34,150-3), (16) 3′-aminoacetophenone (Aldrich13,935-1), (17) 4′-aminoacetophenone (Aldrich A3,800-2), (18)1H-benzotriazole-1-acetonitrile (Aldrich 46,752-9), (19)2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol (Aldrich 42,274-6),(20) 1,1-(1,2-ethane-diyl)bis(3,3,5,5-tetramethylpiperazinone)(commercially available from Goodrich Chemicals), (21)2,2,4-trimethyl-1,2-hydroquinoline (commercially available from MobayChemical), (22) 2-(4-benzoyl-3-hydroxy phenoxy)ethylacrylate, (23)2-dodecyl-N-(1,2,2,6,6-pentamethyl-4-piperidinyl) succinimide(commercially available from Aldrich Chemical Co., Milwaukee, Wis.),(24)2,2,6,6-tetramethyl-4-piperidinyl/β,β,β′,β′-tetramethyl-3,9-(2,4,8,10-tetraoxospiro(5,5)-undecane) diethyl]-1,2,3,4-butane tetracarboxylate(commercially available from Fairmount), (25)N-ρ-ethoxycarbonylphenyl)-N′-ethyl-N′-phenylformadine (commerciallyavailable from Givaudan), (26)6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline (commercially availablefrom Monsanto Chemicals), (27)2,4,6-tris-(N-1,4-dimethylpentyl-4-phenylenediamino)-1,3,5-triazine(commercially available from Uniroyal), (28)2-dodecyl-N-(2,2,6,6-tetramethyl-4-piperidinyl) succinimide(commercially available from Aldrich Chemical Co.), (29)N-(1-acetyl-2,2,6,6-tetramethyl-4-piperidinyl)-2-dodecyl succinimide(commercially available from Aldrich Chemical Co.), (30)[1,2,2,6,6-pentamethyl-4-piperidinyl/β,ββ′,β′-tetramethyl-3,9-(2,4,8,10-tetraoxo-spiro-(5,5)undecane)diethyl]-1,2,3,4-butane tetracarboxylate (commerciallyavailable from Fairmount), (31)[2,2,6,6-tetramethyl-4-piperidinyl)-1,2,3,4-butane tetracarboxylate(commercially available from Fairmount), (32) nickel dibutyl dithiocarbamate (commercially available as UV-Chek AM-105 from Ferro), and thelike, as well as mixtures thereof. The optional UV absorber, whenpresent, is present in the ink in any desired or effective amount,typically no less than about 0.25 percent by weight of the ink, andpreferably no less than about 1 percent by weight of the ink, andtypically no more than about 10 percent by weight of the ink, andpreferably no more than about 5 percent by weight of the ink, althoughthe amount can be outside of these ranges.

Other optional additives to the inks include biocides such as Dowicil150, 200, and 75, benzoate salts, sorbate salts, and the like, presentin an amount of from about 0.0001 to about 4 percent by weight of theink, and preferably from about 0.01 to about 2.0 percent by weight ofthe ink, pH controlling agents such as acids or bases, phosphate salts,carboxylates salts, sulfite salts, amine salts, and the like, present inan amount of from 0 to about 1 percent by weight of the ink andpreferably from about 0.01 to about 1 percent by weight of the ink, orthe like.

The ink compositions of the present invention typically have meltingpoints no lower than about 60° C., preferably no lower than about 70°C., and more preferably no lower than about 80° C., and typically havemelting points no higher than about 160° C., preferably no higher thanabout 140° C., and more preferably no higher than about 120° C.,although the melting point can be outside of these ranges.

The ink compositions of the present invention generally have meltviscosities at the jetting temperature (typically no lower than about75° C., preferably no lower than about 100° C., and more preferably nolower than about 120° C., and typically no higher than about 180° C.,preferably no higher than about 150° C., and more preferably no higherthan about 130° C., although the jetting temperature can be outside ofthese ranges) typically of no more than about 25 centipoise, preferablyno more than about 20 centipoise, and even more preferably no more thanabout 10 centipoise, and typically of no less than about 2 centipoise,preferably no less than about 5 centipoise, and even more preferably noless than about 7 centipoise, although the melt viscosity can be outsideof these ranges. Since image hardness tend to drop with lowerviscosities, it is preferred that the viscosity be as low as possiblewhile still retaining the desired degree of image hardness.

Hardness is a property of solids and plastics that is defined by theirsolidity and firmness as measured by their resistance to indentation byan indenter of fixed shape and size under a static load. The hardness ofimages can be measured with a Digital-Pencil style Durometer, Model211B-00 PTC, obtained from Pacific Transducer Corporation, using ASTMStandard specifications for resistance to penetration with a conical [30degrees included angle] indenter and applying a 1 kilogram load. Thehardness range for materials as measured with this instrument is fromabout 1 to about 100, the latter being the highest measurable value. Itis believed that the images generated with the inks of the presentinvention, after cooling to ambient temperature (typically from about 20to about 25° C., although ambient temperature can be outside of thisrange) will exhibit hardness values of at least about 70 or more.

The inks of the present invention typically undergo, upon heating, achange from a solid state to a liquid state in a period of less thanabout 100 milliseconds, preferably less than about 50 milliseconds, andmore preferably less than about 10 milliseconds, although the time canbe outside of these ranges. There is no necessary lower limit on thisperiod of time for the inks; it is believed that practically achievablelower limits are around 5 milliseconds, although, if practicallyachievable, lower periods of time are acceptable.

The inks of the present invention typically exhibit acoustic-loss valuesof no more than about 100 decibels per millimeter, preferably no morethan about 60 decibels per millimeter, and more preferably no more thanabout 40 decibels per millimeter, although the acoustic-loss value canbe outside of these ranges. There is no necessary lower limit onacoustic-loss value for the inks; it is believed that practicallyachievable lower limits are around 10 decibels per millimeter, although,if practically achievable, lower acoustic-loss values are acceptable.Acoustic-loss can be measured by placing a sample of the material to bemeasured between two transducers with the temperature set at about 150°C. The samples are allowed to equilibrate at 150° C. for five minutes.The two transducers are then brought together to maximize the acousticsignal. The amplitude and the position of the signals are recorded. Thetwo transducers are then separated by a distance varying from about 25.4microns to about 125.4 microns, recording each time the amplitude andthe position of the signal. Preferably, each measurement is performedthree times, and three samples of the same material are measured. Theattenuation decibels per millimeter is then calculated by rationing theamplitude values obtained at different separation distances.

The inks of the present invention typically exhibit a conductivity of noless than about 2 log(picomho/cm), preferably no less than about 6log(picomho/cm), more preferably no less than about 6.5 log(picomho/cm),and even more preferably no less than about 7 log(picomho/cm), althoughthe conductivity can be outside of these ranges. While there is no upperlimit on conductivity, typical conductivity values generally do notexceed about 9 log(picomho/cm). Conductivity can be measured under meltconditions (typically at about 150° C.) by placing an aluminum electrodein the molten ink and reading the resistivity output on a GenRad 1689precision RLC Digibridge at a frequency of 1 kiloHertz). Theconductivity of the material is measured in terms of the reciprocal ofresistivity, which is the capacity for electrical resistance.

The inks of the present invention exhibit substantial transparency. Theimages generated with the inks typically exhibit haze values of no morethan about 25, preferably no more than about 10, and preferably no morethan about 5, although the haze value can be outside of these ranges.There is no required lower limit on haze values. Haze values can bemeasured on images printed with the ink on uncoated polyester, such asMYLAR®, with a Haze meter XL-211, HAZEGARD® System obtained from PacificScientific Company.

The inks of the present invention generate images with desirable creaseresistance. The images generated with the inks typically exhibit creasevalues of no more than about 0.6 millimeters, preferably no more thanabout 0.2 millimeters, and more preferably no more than about 0.1millimeters, although the crease value can be outside of these ranges.There is no lower limit on crease values; ideally, this value is zero.The average width of the creased image can be measured by printing animage on paper, followed by (a) folding inwards the printed area of theimage, (b) passing over the folded image a standard TEFLON® coatedcopper roll 2 inches in width, 3 inches in outer diameter, 2.25 inchesin inner diameter, and weighing 860 grams, (c) unfolding the paper andwiping the loose ink from the creased imaged surface with a cotton swab,and (d) measuring the average width of the ink free creased area with animage analyzer. The crease value can also be reported in terms of area,especially when the image is sufficiently hard to break unevenly oncreasing. Measured in terms of area, crease values of 60 millimeterscorrespond to about 0.6, crease values of 40 millimeters correspond toabout 0.4, crease values of 10 millimeters correspond to about 0.1, andthe like.

The ink compositions of the present invention can be prepared by anydesired or suitable method. For example, the ink ingredients can bemixed together, followed by heating, typically to a temperature of fromabout 100 to about 140° C., although the temperature can be outside ofthis range, and stirring until a homogeneous ink composition isobtained, followed by cooling the ink to ambient temperature (typicallyfrom about 20 to about 25° C.). The inks of the present invention aresolid at ambient temperature.

The present invention is also directed to a process which entailsincorporating an ink of the present invention into an ink jet printingapparatus, melting the ink, and causing droplets of the melted ink to beejected in an imagewise pattern onto a recording sheet. In one preferredembodiment, the printing apparatus employs an acoustic ink jet process,wherein droplets of the ink are caused to be ejected in imagewisepattern by acoustic beams. In a particularly preferred embodiment, theprinting apparatus employs an acoustic ink jet printing process whereindroplets of the ink are formed by acoustic beams without imparting asubstantial velocity component toward the print medium, using a dropletforming force that is sufficient only to form the ink droplets, and theprinting process further comprises generating an electric field to exertan electrical force different from the droplet forming force on the inkdroplets to move the ink droplets toward the print medium, andcontrolling the electrical force exerted on the formed complete inkdroplets by the electric field.

Any suitable substrate or recording sheet can be employed, includingplain papers such as Xerox® 4024 papers, Xerox® Image Series papers,Courtland 4024 DP paper, ruled notebook paper, bond paper, silica coatedpapers such as Sharp Company silica coated paper, JuJo paper, and thelike, transparency materials, fabrics, textile products, plastics,polymeric films, inorganic substrates such as metals and wood, and thelike. In a preferred embodiment, the process entails printing onto aporous or ink absorbent substrate, such as plain paper.

The inks of the present invention are particularly suitable for printingprocesses wherein the printing substrate, such as paper, transparencymaterial, or the like, is heated during the printing process. Whentransparency substrates are employed, temperatures typically are nohigher than from about 100 to about 110° C., since the polyestercommonly employed as the base sheet in transparency sheets tends todeform at higher temperatures. Specially formulated transparencies andpaper substrates can, however, tolerate higher temperatures, andfrequently are suitable for exposure to temperatures of 150° C. or even200° C. in some instances. Typical heating temperatures are from about40 to about 140° C., and preferably from about 60 to about 95° C.,although the temperature can be outside of these ranges.

Specific embodiments of the invention will now be described in detail.These examples are intended to be illustrative, and the invention is notlimited to the materials, conditions, or process parameters set forth inthese embodiments. All parts and percentages are by weight unlessotherwise indicated.

Acoustic-loss measurements in the Examples were measured by placingsamples of the materials between the two transducers with thetemperature set at 150° C. The samples were allowed to equilibrate at150° C. for five minutes. The two transducers were then brought togetherto maximize the acoustic signal. The amplitude and the position of thesignals were recorded. The two transducers were then separated by adistance varying from 25.4 microns to 125.4 microns, recording each timethe amplitude and the position of the signal. Each measurement wasperformed three times, and three samples of each material were measured.The attenuation decibels per millimeter was then calculated by ratioingthe amplitude values obtained at different separation distances.

Optical density values in the Examples were obtained on a PacificSpectrograph Color System. The system consists of two major components,an optical sensor and a data terminal. The optical sensor employs a 6inch integrating sphere to provide diffuse illumination and 8 degreesviewing. This sensor can be used to measure both transmission andreflectance samples. When reflectance samples are measured, a specularcomponent may be included. A high resolution, full dispersion, gratingmonochromator was used to scan the spectrum from 380 to 720 nanometers.The data terminal features a 12 inch CRT display, numeric keyboard forselection of operating parameters and the entry of tristimulus values,and an alphanumeric keyboard for entry of product standard information.

Lightfast values in the Examples were measured in a Mark V LightfastTester, obtained from Microscal Company, London, England.

Waterfast values in the Examples were obtained from the optical densitydata recorded before and after washing the images with water at 25° C.for five minutes.

Viscosity values in the Examples were measured at 150° C. with a StressRheometer, obtained from Cari-Med, Model CSL 100. All experiments wereperformed at a shear rate of 1250 s⁻¹.

Conductivity values in the Examples were measured under melt conditionsat 150° C. by placing an aluminum electrode in the melt and reading theresistivity output on a GenRad 1689 precision RLC Digibridge at afrequency of 1 kiloHertz. Conductivity was calculated from theresistivity data.

Crease values in the Examples were measured on solid area images printedon paper by (a) folding inwards the printed area of the image, (b)passing over the folded image a standard TEFLON® coated copper roll 2inches in width, 3 inches in outer diameter, 2.25 inches in innerdiameter, and weighing 860 grams, (c) unfolding the paper and wiping theloose ink from the creased imaged surface with a cotton swab, and (d)measuring the average width of the ink free creased area with an imageanalyzer.

Haze values in the Examples were measured on images printed on uncoatedpolyester (such as MYLAR®) with a Haze meter XL-211, HAZEGARD® System,obtained from Pacific Scientific Company.

EXAMPLE I

A black phase-change ink was prepared by mixing 50 percent by weight1-dodecyl pyridinium chloride hydrate (conductive quaternary pyridinecompound; Aldrich 27,860-2; conductivity 9.0 log(picomho/cm);acoustic-loss value 35 decibels per millimeter; melting point 70° C.), 5percent by weight poly(4-vinylpyridinium-ρ-toluene sulfonate (polymericpyridine ink binder; Aldrich 36,273-5), 30 percent by weight2,2′-dipyridyl amine (viscosity modifier; Aldrich D21,630-5;acoustic-loss value 23 decibels per millimeter; melting point 96° C.), 5percent by weight 4′-benzyloxy-2′-hydroxy-3′-methyl acetophenone (UVabsorber; Aldrich 29,884-0), 5 percent by weight2,4-bis(trifluoromethyl)benzoic acid (antioxidant; Aldrich 37,058-4),and 5 percent by weight Neozapon Black X51 dye (C.I. Solvent Black; C.I.12195; obtained from BASF). The mixture was heated to a temperature of140° C., stirred for a period of about 60 minutes until it formed ahomogeneous solution, and subsequently cooled to 25° C. This inkexhibited a viscosity of 8.5 centipoise at 150° C., an acoustic-lossvalue of 60 decibels per millimeter, and a conductivity of 8.5log(picomho/cm) at 150° C.

EXAMPLE II

A blue phase-change ink was prepared by mixing 50 percent by weight1-ethyl-3-hydroxy pyridinium bromide (conductive quaternary pyridinecompound; Aldrich 19,264-3; conductivity 8.7 log(picomho/cm);acoustic-loss value 33 decibels per millimeter; melting point 106° C.),5 percent by weight poly(4-vinylpyridinium-ρ-toluene sulfonate)(polymeric pyridine ink binder; Aldrich 36,273-5), 30 percent by weight2,2′-dipyridyl amine (viscosity modifier; Aldrich D21,630-5;acoustic-loss value 23 decibels per millimeter; melting point 96° C.), 5percent by weight 4′-benzyloxy-2′-hydroxy-3′-methyl acetophenone (UVabsorber; Aldrich 29,884-0), 5 percent by weight2,4-bis(trifluoromethyl)benzoic acid (antioxidant; Aldrich 37,058-4),and 5 percent by weight Sudan Blue 670 dye (C.I. 61554; obtained fromBASF). The mixture was heated to a temperature of 140° C., stirred for aperiod of about 60 minutes until it formed a homogeneous solution, andsubsequently cooled to 25° C. This ink had a viscosity of 8.7 centipoiseat 150° C., an acoustic-loss value of 62 decibels per millimeter, and aconductivity of 8.3 log(picomho/cm at 150° C.

EXAMPLE III

A yellow phase-change ink was prepared by mixing 50 percent by weightcetyl pyridinium bromide monohydrate (conductive quaternary pyridinecompound; Aldrich 28,531-5; conductivity 8.8 log(picomho/cm);acoustic-loss value 30 decibels per millimeter; melting point 70° C.), 5percent by weight poly(4-vinylpyridinium-ρ-toluene sulfonate) (polymericpyridine ink binder; Aldrich 36,273-5), 30 percent by weight2,2′-dipyridyl amine (viscosity modifier; Aldrich D21,630-5;acoustic-loss value 23 decibels per millimeter; melting point 96° C.), 5percent by weight 4′-benzyloxy-2′-hydroxy-3′-methyl acetophenone (UVabsorber; Aldrich 29,884-0), 5 percent by weight2,4-bis(trifluoromethyl)benzoic acid (antioxidant; Aldrich 37,058-4);and 5 percent by weight Sudan Yellow 146 dye (C.I. 12700; obtained fromBASF). The mixture was heated to a temperature of 140° C., stirred for aperiod of about 60 minutes until it formed a homogeneous solution, andsubsequently cooled to 25° C. This ink exhibited a viscosity of 8.4centipoise at 150° C., an acoustic-loss value of 61 decibels permillimeter, and a conductivity of 8.4 log(picomho/cm) at 150° C.

EXAMPLE IV

A red phase-change ink was prepared by mixing 50 percent by weight1-ethyl-4-phenyl pyridinium iodide (conductive quaternary pyridinecompound; Aldrich 36,208-5; conductivity 8.3 log(picomho/cm;acoustic-loss value 39 decibels per millimeter; melting point 124° C.),5 percent by weight poly(4-vinylpyridinium-ρ-toluene sulfonate)(polymeric pyridine ink binder; Aldrich 36,273-5), 30 percent by weight2,2′-dipyridyl amine (viscosity modifier; Aldrich D21,630-5;acoustic-loss value 23 decibels per millimeter; melting point 96° C.), 5percent by weight 4′-benzyloxy-2′-hydroxy-3′-methyl acetophenone (UVabsorber; Aldrich 29,884-0), 5 percent by weight2,4-bis(trifluoromethyl)benzoic acid (antioxidant; Aldrich 37,058-4),and 5 percent by weight Sudan Red 462 dye (C.I. 26050; obtained fromBASF). The mixture was heated to a temperature of 140° C., stirred for aperiod of about 60 minutes until it formed a homogeneous solution, andsubsequently cooled to 25° C. This ink exhibited a viscosity of 8.8centipoise at 150° C., an acoustic-loss value of 64 decibels permillimeter, and a conductivity of 8.4 log(picomho/cm) at 150° C.

EXAMPLE V

Each of the inks prepared as described in Examples I through IV wasincorporated into an acoustic ink jet printing test fixture utilizingthe ejection mechanism disclosed in J. Appl. Phys., 65(9), May 1, 1989,and references therein, the disclosures of each of which are totallyincorporated herein by reference. A jetting frequency of 160 MHz wasused to generate drops of about 2 picoliters, up to 12 drops per pixelat 600 spi. The images formed on paper exhibited excellent colorquality, optical density values of 2.20 (black), 1.80 (cyan), 1.85(magenta), and 1.45 (yellow), sharp edges, lightfast values of 96.5%(black), 97.5% (cyan), 96% (magenta), and 98% (yellow), and waterfastvalues of 96% (black), 95.% (cyan), (97% (magenta), and 95% (yellow).The images obtained with these conductive inks on paper were folded andcreased. The crease values (measured in terms of area and subsequentlyconverted to millimeters) were 0.06 (black), 0.09 (cyan), 0.09(magenta), and 0.06 (yellow).

EXAMPLE VI

A black phase-change ink was prepared by mixing 50 percent by weight1-dodecyl pyridinium chloride hydrate (conductive quaternary pyridinecompound; Aldrich 27,860-2; conductivity 9.0 log(picomho/cm);acoustic-loss value 35 decibels per millimeter; melting point 70° C.), 5percent by weight poly(4-vinylpyridinium-co-butyl methacrylate)containing 50 percent by weight butyl methacrylate (polymeric pyridineink binder; obtained from Scientific Polymer Products), 30 percent byweight 1,2-bis(4-pyridyl)ethylene (viscosity modifier; Aldrich B5,260-3;acoustic-loss value 25 decibels per millimeter; melting point 118° C.),5 percent by weight 4′-piperazinoacetophenone (UV absorber; Aldrich13,646-8), 5 percent by weight 2,6-dibromo fluorophenol (antioxidant;Aldrich 26,003-7), and 5 percent by weight Neozapon Black X51 dye (C.I.Solvent Black; C.I. 12195; obtained from BASF). The mixture was heatedto a temperature of 140° C., stirred for a period of about 60 minutesuntil it formed a homogeneous solution, and subsequently cooled to 25°C. This ink exhibited a viscosity of 8.7 centipoise at 150° C., anacoustic-loss value of 63.5 decibels per millimeter, and a conductivityof 8.3 log(picomho/cm) at 150° C.

EXAMPLE VII

A blue phase-change ink was prepared by mixing 50 percent by weight1-ethyl-3-hydroxy pyridinium bromide (conductive quaternary pyridinecompound; Aldrich 19,264-3; conductivity 8.7 log(picomho/cm);acoustic-loss value 33 decibels per millimeter; melting point 106° C.),5 percent by weight poly(4-vinylpyridinium-co-butyl methacrylate)containing 50 percent by weight butyl methacrylate (polymeric pyridineink binder; obtained from Scientific Polymer Products), 30 percent byweight 1,2-bis(4-pyridyl)ethylene (viscosity modifier; Aldrich B5,260-3;acoustic-loss value 25 decibels per millimeter; melting point 118° C.),5 percent by weight 4′-piperazinoacetophenone (UV absorber; Aldrich13,646-8), 5 percent by weight 2,6-dibromo fluorophenol (antioxidant;Aldrich 26,003-7), and 5 percent by weight Sudan Blue 670 dye (C.I.61554; obtained from BASF). The mixture was heated to a temperature of140° C., stirred for a period of about 60 minutes until it formed ahomogeneous solution, and subsequently cooled to 25° C. This inkexhibited a viscosity of 8.8 centipoise at 150° C., an acoustic-lossvalue of 65.5 decibels per millimeter, and a conductivity of 8.2log(picomho/cm) at 150° C.

EXAMPLE VIII

A yellow phase-change ink was prepared by mixing 50 percent by weightcetyl pyridinium bromide monohydrate (conductive quaternary pyridinecompound; Aldrich 28,531-5; conductivity 8.8 log(picomho/cm);acoustic-loss value 30 decibels per millimeter; melting point 70° C.), 5percent by weight poly(4-vinylpyridinium-co-butyl methacrylate)containing 50 percent by weight butyl methacrylate (polymeric pyridineink binder; obtained from Scientific Polymer Products), 30 percent byweight amino pyrazine (viscosity modifier; Aldrich A7,695-8;acoustic-loss value 23 decibels per millimeter; melting point 120° C.),5 percent by weight 4′-piperidino acetophenone (UV absorber; Aldrich11,972-5), 5 percent by weight 2,6-dibromo fluorophenol (antioxidant;Aldrich 26,003-7), and 5 percent by weight Sudan Yellow 146 dye (C.I.12700; obtained from BASF). The mixture was heated to a temperature of140° C., stirred for a period of about 60 minutes until it formed ahomogeneous solution, and subsequently cooled to 25° C. This inkexhibited a viscosity of 8.4 centipoise at 150° C., an acoustic-lossvalue of 67 decibels per millimeter, and a conductivity of 8.2log(picomho/cm) at 150° C.

EXAMPLE IX

A red phase-change ink was prepared by mixing 50 percent by weight1-ethyl-4-phenyl pyridinium iodide, (Aldrich 36,208-5; conductivity 8.3log(picomho/cm); acoustic-loss value 39 decibels per millimeter; meltingpoint 124° C.), 5 percent by weight poly(4-vinylpyridinium-co-butylmethacrylate) containing 50 percent by weight butyl methacrylate(polymeric pyridine ink binder; obtained from Scientific PolymerProducts), 30 percent by weight 2,3-dimethylquinoxaline (viscositymodifier; Aldrich D18,497-7; acoustic-loss value 25 decibels permillimeter; melting point 105° C.), 5 percent by weight 4′-piperidinoacetophenone (UV absorber; Aldrich 11,972-5), and 5 percent by weightSudan Red 462 dye (C.I. 26050; obtained from BASF). The mixture washeated to a temperature of 140° C., stirred for a period of about 60minutes until it formed a homogeneous solution, and subsequently cooledto 25° C. This ink exhibited a viscosity of 8.7 centipoise at 150° C.,an acoustic-loss value of 68 decibels per millimeter, and a conductivityof 8.1 log(picomho/cm) at 150° C.

EXAMPLE X

Each of the inks prepared as described in Examples VI through IX wasincorporated into an acoustic ink jet printing test fixture and testedas described in Example V. The images formed on paper exhibitedexcellent color quality, optical density values of 2.15 (black), 1.85(cyan), 1.85 (magenta), and 1.48 (yellow), sharp edges, lightfast valuesof 96% (black), 97.5% (cyan), 96% (magenta), and 97% (yellow), andwaterfast values of 95% (black), 94% (cyan), 95% (magenta), and 95%(yellow). The images obtained with these conductive inks on paper werefolded and creased. The crease values (measured in terms of area andsubsequently converted to millimeters) were 0.05 (black), 0.09 (cyan),0.10 (magenta), and 0.06 (yellow).

Other embodiments and modifications of the present invention may occurto those of ordinary skill in the art subsequent to a review of theinformation presented herein; these embodiments and modifications, aswell as equivalents thereof, are also included within the scope of thisinvention.

What is claimed is:
 1. An ink composition comprising (a) an ink vehiclewhich comprises a conductive pyridinium compound having a melting pointof no lower than about 60° C. and no higher than about 155° C., (b) aviscosity modifier which is a pyridine compound, a pyrimidine compound,a pyrazine compound, a pyridazine compound, or mixtures thereof, saidpyridine, pyrimidine, pyrazine, or pyridazine compounds having a meltingpoint of no lower than about 60° C. and no higher than about 155° C.,(c) a binder which is a polymeric pyridine or pyridinium compound; (d) acolorant, (e) an optional antioxidant, and (f) an optional UV absorber.2. An ink composition according to claim 1 wherein the ink has a meltingpoint of no lower than about 60° C. and no higher than about 160° C. 3.An ink composition according to claim 1 wherein the ink has a meltviscosity at jetting temperature of no higher than about 25 centipoise.4. An ink composition according to claim 1 wherein the ink undergoes,upon heating, a change from a solid state to a liquid state in a periodof no more than about 100 milliseconds.
 5. An ink composition accordingto claim 1 wherein the ink exhibits an acoustic-loss value of no morethan about 100 decibels per millimeter.
 6. An ink composition accordingto claim 1 wherein the ink exhibits a conductivity of no less than about6 log(picomho/cm).
 7. An ink composition according to claim 1 whereinimages generated with the ink exhibit a haze value of no more than about25.
 8. An ink composition according to claim 1 wherein the ink vehicleis present in the ink in an amount of no less than about 0.5 percent byweight of the ink and no more than about 80 percent by weight of theink.
 9. An ink composition according to claim 1 wherein the ink vehicleis a 1-propyl pyridinium salt, a 1-ethyl-3-hydroxy pyridinium salt, a1-ethyl-4-phenyl pyridinium salt, a 1-ethyl-4-(methoxy carbonyl)pyridinium salt, pyridinium 3-nitrobenzene sulfonate,pyridinium-ρ-toluene sulfonate, pyridinium trifluoroacetate, a1-heptyl-4-(4-pyridyl) pyridinium salt, a cetyl pyridinium salt, a1-dodecyl pyridinium salt, or mixtures thereof.
 10. An ink compositionaccording to claim 1 wherein the viscosity modifier is present in theink in an amount of no less than about 1 percent by weight of the inkand no more than about 70 percent by weight of the ink.
 11. An inkcomposition according to claim 1 wherein the viscosity modifier is2-hydroxy pyridine, 3-hydroxy pyridine, 2-pyridine carboxamide,2-pyridine aldoxime, 4,4′-dipyridyl, 2,2′-dipyridyl amine,4,4′-dipyridyl disulfide, 1,2-bis(4-pyridyl) ethane, 1,2-bis(4-pyridyl)ethylene, 3-amino-2-chloropyridine, 5-amino-2-chloropyridine,2,3-diaminopyridine, 2,6-diaminopyridine, 2,5-dibromopyridine,3,5-dibromopyridine, 2,6-dibromopyridine, 2,6-dichloropyridine, 2-benzylaminopyridine, 3,4-dipyridine dicarbonitrile, 2,6-pyridinedicarboxaldehyde, 3,4-pyridine dicarboxylic anhydride, 2,6-pyridinedimethanol, 3-hydroxy-2-nitropyridine, 2-methoxy-5-nitropyridine,dimethyl 2,6-pyridine dicarboxylate, 2-amino-3,5-dichloropyridine,2-amino-3,5-dibromopyridine, 2-(2-aminoethyl amino)-5-nitropyridine,2,6-bis(chloromethyl) pyridine, 2-chloro-6-methoxy-3-nitropyridine,2-chloro-6-methyl-3-pyridine carbonitrile,3,5-diacetyl-2,6-dimethylpyridine, diethyl (6-methyl-2-pyridyl aminomethylene) malonate, 3-hydroxy-6-methyl-2-nitropyridine,1-(2-pyridyl)-2-(4-pyridyl) ethylene,1-acetyl-1H-1,2,3-triazolo-pyridine, di-2-pyridyl thionocarbonate,2-aminopyrimidine, 2-amino-4,6-dimethoxypyrimidine,6-chloro-2,4-dimethoxypyrimidine,4,6-dichloro-2-methylthio-5-phenylpyrimidine,4,6-dichloro-5-nitropyrimidine, amino pyrazine,3-chloro-6-methoxypyridazine, 3,6-dichloro-4-methylpyridazine),2,3-dimethylquinoxaline, or mixtures thereof.
 12. An ink compositionaccording to claim 1 wherein the binder is present in the ink in anamount of no less than about 0.5 percent by weight of the ink and nomore than about 18 percent by weight of the ink.
 13. An ink compositionaccording to claim 1 wherein the binder is poly(4-vinylpyridinium-ρ-toluene sulfonate), poly(4-vinyl pyridinium tribromide),poly(4-vinyl pyridinium polyhydrogen fluoride), poly(4-vinylpyridinium-co-butyl methacrylate), polyvinyl pyridine, or mixturesthereof.
 14. An ink composition according to claim 1 wherein thecolorant is a dye.
 15. An ink composition according to claim 1containing an antioxidant in an amount of no less than about 0.25percent by weight of the ink and no more than about 10 percent by weightof the ink.
 16. An ink composition according to claim 1 containing a UVabsorber in an amount of no less than about 0.25 percent by weight ofthe ink and no more than about 10 percent by weight of the ink.
 17. Anink composition according to claim 1 wherein the colorant is a pigment.18. A printing process which comprises incorporating an ink according toclaim 1 into an ink jet printing apparatus, melting the ink, and causingdroplets of the melted ink to be ejected in an imagewise pattern onto arecording sheet.
 19. A process according to claim 18 wherein theprinting apparatus employs an acoustic ink jet process, wherein dropletsof the ink are caused to be ejected in imagewise pattern by acousticbeams.
 20. A process according to claim 18 wherein the printingapparatus employs an acoustic ink jet printing process wherein dropletsof the ink are formed by acoustic beams without imparting a substantialvelocity component toward the print medium, using a droplet formingforce that is sufficient only to form the ink droplets, and wherein theprinting process further comprises generating an electric field to exertan electrical force different from the droplet forming force on the inkdroplets to move the ink droplets toward the print medium, andcontrolling the electrical force exerted on the formed complete inkdroplets by the electric field.